Wireless telecommunication systems are known. In such systems, mobile communication devices known as user equipment (for example, mobile telephones) are operable to communicate with base stations provided by network providers.
In known wireless telecommunication systems, radio coverage is provided to network connectable devices, such as mobile telephones, or wireless devices such as iPads or other similar tablets, within areas known as cells. A base station is located in each cell to provide radio coverage. Typically, network connectable devices in each cell are operable to receive information and data from a base station and to transmit information and data to a base station.
User equipment roam through the wireless communications system. A number of base stations are provided and are distributed geographically in order to provide a wide area of coverage to user equipment.
When user equipment is within an area served by a base station, communications may be established between the user equipment and the base station over associated radio links. Each base station typically supports a number of sectors within the geographical area of service. Typically, a different antenna within a base station supports each associated sector. Each base station has multiple antennas.
Traditional base stations provide coverage in relatively large geographical areas and those cells are often referred to as macro cells. It is possible to provide a heterogeneous network (HetNet) where smaller sized cells are provided within macro cells. Such smaller sized cells are sometimes referred to as micro cells, pico cells or femto cells. One way to establish a small cell is to provide a small cell base station that provides coverage having a relatively limited range within the coverage area of the macro cell. The transmission power of a small cell base station is relatively low and, hence, each small cell provides a small coverage area compared to that of a macro cell and covers, for example, an office or a home.
Such small cells are typically provided where the communications coverage provided by the macro cell is poor or where a user wishes to use an alternative communications link provided locally, by the small cell base station, to communicate with the core network, and/or to increase capacity or user throughput within a network.
Deployment of small cells in a wireless communication network can assist a network in relation to handling capacity in high traffic areas, for example, so-called hot spot areas. An ability to offload traffic to a small cell or cells located in a high traffic area of a network may be particularly useful to a network operator. In some cases, “dual connectivity” may be offered such that a user is configured to allow communication with two base stations such as, for example, a macro cell base station and a small cell base station. A number of dual connectivity implementations can be configured, each may offer different benefits.
With dual connectivity, user equipment is connected to both a macro cell provided by a master base station (MeNB) and a small cell provided by a secondary base station (SeNB). There are currently two architectural options being considered 1A and 3C. FIG. 1 illustrates the radio protocol stack for a bearer. FIG. 2 illustrates architectural option 1A, where a bearer is handled entirely in the small cell (i.e. all the radio access network (RAN) protocol layers for the bearer, packet data convergence protocol (PDCP), radio link control (RLC) and medium access control (MAC)) are in the SeNB. Security for the bearer is handled in the PDCP layer in the SeNB. FIG. 3 shows the encryption algorithm used for the bearer. The encryption algorithm uses a COUNT (or the packet number) as an input. The COUNT consists of two parts, the hyper frame number (HFN) and the sequence number (SN). The SN is included in each packet. The HFN is not included in order to reduce the packet size, but it is instead maintained within the user equipment and the network. This maintains synchronization of the COUNT in the network and the user equipment even if a number of packets less than the sequence number size is lost. Another input to the encryption algorithm is a 5 bit BEARER identity.
Although dual connectivity deployments may offer advantages, unexpected consequences of such deployments may occur. It is desired to address those consequences.